TWI464867B - Solid-state image pickup device and method for manufacturing same, and image pickup apparatus - Google Patents

Description

Solid-state image pickup device and manufacturing method thereof, and image pickup device

The present invention relates to a solid-state image pickup device and a method of fabricating the same, and to an image pickup device including the solid-state image pickup device.

In solid-state image pickup devices, in order to compensate for the reduction in charge storage capacity due to the miniaturization of the pixel being advanced, it has been proposed to form a conductivity type under the charge storage region in addition to the charge storage region of the existing sensor unit. The same impurity area.

In addition, a charge storage unit has been proposed in which ions having different energies are injected into a lower portion of a charge storage region to form a plurality of impurity regions, followed by combination with a known charge storage region (see, for example) Japanese Patent Laid-Open No. 2002-164529).

In this patent application, a CCD (Charge Coupled Device) solid-state image pickup device is described. With regard to a CMOS (Complementary Metal Oxide Semiconductor) solid-state image pickup device, a plurality of impurity regions can be formed under the storage image pickup region of the sensor unit, thereby configuring a charge storage unit.

A schematic configuration diagram (cross-sectional view) of the CMOS solid-state image pickup device configured in this manner is shown in FIGS. 5A and 5B. 5A is a cross-sectional view at one side perpendicular to a transfer gate, and FIG. 5B is a cross-sectional view taken along line XX' of FIG. 5A.

It is to be noted that although a first charge storage unit and a second charge storage unit are mentioned in the laid-open patent application No. 2002-164529, the charge storage region hitherto known is referred to herein as the main charge storage region. And this lower impurity region is referred to as a charge storage subregion.

The solid-state image pickup device shown in FIGS. 5A and 5B is configured such that individual pixels are isolated by the P ⁺ device isolation region 53 and the photodiode (PD) and charge transfer portion of the sensor unit are formed. The interior is isolated by the isolation region 53 of the device. In the figures, a semiconductor substrate (i.e., a semiconductor substrate or a semiconductor substrate and a semiconductor epitaxial layer formed thereon) is indicated by 51, and is instructed by 52 to be buried in the semiconductor substrate. The p ^- semiconductor well region in 51. An overflow barrier is formed by the semiconductor well region 52.

In this solid-state image pickup device, an n-type charge storage sub-region is formed particularly under the n ⁺ -type charge storage region 54 of the sensor unit. The charge storage sub-region is composed of three n-type impurity regions, which include a first charge storage sub-region 61, a second charge storage sub-region 62, and a third charge storage device as viewed from below. Area 63.

The charge storage sub-region formed by the first charge storage sub-region 61, the second charge storage sub-region 62, and the third charge storage sub-region 63 acts to increase the state in which the charge storage region 54 is formed only deep. Charge storage capacity.

In this way, it is possible to compensate for the decrease in charge storage capacity and to suppress the decrease in sensitivity caused by miniaturization of the pixel when miniaturizing the pixel.

In addition, photoelectrons that are photoelectrically converted at deep regions of the photodiode can be efficiently transferred.

The first charge storage sub-region 61, the second charge storage sub-region 62, and the third charge storage sub-region 63 may be sequentially formed by ion implantation of n-type impurities of different energy levels.

The potential distribution diagram at the cross section of Fig. 5B is shown in Fig. 6.

As shown in FIG. 6, the potential distribution extending in the depth direction is formed by the formation of the charge storage sub-regions 61, 62, 63.

When the n-type impurity is subjected to a multi-stage cycle of ion implantation to form a charge storage sub-region, this potential along this depth can be designed.

As will be seen from FIG. 5A, charge storage sub-regions 61, 62, 63 formed for the purpose of improving sensitivity are formed only below the charge storage region 54 (ie, inside the photodiode).

This is for the purpose of suppressing white point deterioration and also suppressing overflow of stored charges due to pinning degradation at the deep portion of the photodiode.

Also in this structure having this charge storage sub-region, as the pixel is pushed down, the effective area of the photodiode is reduced.

At the cross section of Fig. 5B, the distance between the p ⁺ device isolation regions becomes narrower than the distance at the cross section of Fig. 5A.

Therefore, in the deep portion of the photodiode, since the effective concentration of the p-type impurity caused by the device isolation region 53 and the semiconductor well region 52 is increased, the potential is necked. This situation is illustrated with reference to FIG.

7 shows the device isolation region 53 and the semiconductor well region 52 (both of which are p-type impurity regions) after the cross-sectional structure of FIG. 5B is superimposed on the potential map of FIG.

As shown in FIG. 7, the increased effective concentration of the p-type impurity regions (i.e., device isolation region 53 and semiconductor well region 52) causes the n-type impurity region to be necked relative to its potential, as indicated by the arrows.

This results in the possibility of extending the depletion layer to this depth and the sensitivity can be lower than the design value.

Of course, as illustrated in Japanese Laid-Open Patent Application No. 2002-164529, the provision of the charge storage sub-region is mitigated by the effect of extending the potential in the depth direction when compared with the case where the charge storage region is formed only deep. The potential is necked.

However, in combination with other advances in pixel miniaturization, it is not desirable to provide only charge storage sub-regions.

Therefore, further innovation becomes necessary to ensure sensitivity associated with pixel miniaturization.

In order to solve the above problems, embodiments of the present technology are intended to provide a solid-state image pickup device and a method of fabricating the same, wherein if the pixel miniaturization is further advanced, satisfactory sensitivity can be ensured, and a solid-state image pickup device including the same is also provided. Solid-state image pickup device.

The solid-state image pickup device of this embodiment of the present invention is constituted by a pixel including a sensor unit in which the sensor unit is capable of photoelectric conversion.

A semiconductor substrate and a charge storage region formed in the semiconductor substrate and serving as one of a first conductivity type of a sensor unit are included.

Further comprising a charge storage sub-region made of an impurity region of the first conductivity type, the charge storage sub-region being formed in the plurality of layers in the semiconductor substrate under the charge storage region serving as a main charge storage region And wherein at least one or more of the plurality of layers are formed completely across the pixel.

Further, one of the device isolation regions formed in the semiconductor substrate isolates the pixels from each other and is made of one impurity region of a second conductivity type.

A method for fabricating a solid-state image pickup device according to an embodiment of the present invention is a method of constituting a pixel, each of which includes a sensor unit capable of photoelectric conversion.

The method includes forming a charge storage sub-region made of one impurity region of a first conductivity type completely across a pixel in a semiconductor substrate, and forming a charge storage made of one impurity region of the first conductivity type A plurality of layers of a subregion.

In addition, the method includes: forming a device isolation region in the semiconductor substrate, the device isolation region isolating the pixel and is made of an impurity region of a second conductivity type; and in the semiconductor substrate, the charge storage subregion A charge storage region of the first conductivity type serving as a sensor unit is formed on the plurality of layers.

The image pickup apparatus according to an embodiment of the present invention includes: a focusing optical unit that focuses incident light; a solid-state image pickup device that receives incident light that is focused by the focusing optical unit and subjected to photoelectric conversion; and a signal processing unit A signal obtained by photoelectric conversion performed in the solid-state image pickup device is processed.

According to the solid-state image pickup device of the embodiment of the present invention, a plurality of layers of the charge storage sub-region made of one impurity region of the first conductivity type are formed in the semiconductor substrate to serve as a main charge storage region. Below the charge storage region of the first conductivity type. When compared with the case where only one charge storage region is formed deep, the potential can be extended in the depth direction by providing the charge storage subregion.

In addition, since at least one or more of the plurality of layers of the charge storage sub-region are formed completely across the pixel, one of the impurities of the first conductivity type at the depth of the sensor unit can be increased. dose. This results in a reduction in the potential necking of the impurity region of the second conductivity type from around the charge storage subregion and allows one of the potential distributions in the sensor unit to expand along a depth direction and also allows the sensor The depletion layer in the cell extends along a depth direction whereby an amount of saturated charge in the sensor unit can be increased.

A method for fabricating a solid-state image pickup device according to an embodiment of the present invention, a charge storage sub-region formed of one impurity region of a first conductivity type is formed across a pixel in a semiconductor substrate, and is formed by a plurality of layers of the charge storage sub-region made of one impurity region of the first conductivity type, the plurality of layers including the charge storage sub-region formed entirely across the pixels. This enables a solid-state image pickup device to be fabricated to have a structure in which a depletion layer in a sensor unit extends in a depth direction, thereby ensuring an increased saturation charge amount in one of the sensor units .

According to an image pickup apparatus of an embodiment of the present invention, the solid-state image pickup device includes the solid-state image pickup device of the present invention such that a saturation charge amount in the sensor unit can be increased in the image pickup device, thereby ensuring The sensitivity of people's satisfaction.

According to an embodiment of the present invention, the solid-state image pickup device enables an amount of saturation charge in one of the sensor units to be increased, thereby improving the sensitivity of the sensor unit.

Therefore, if the pixel miniaturization is advanced, satisfactory sensitivity can be ensured. Therefore, the pixel can be miniaturized, in which there is a possibility that the number of pixels can be increased and the size reduction of the solid-state image pickup device can be achieved.

According to an embodiment of the present invention, if the number of pixels of a solid-state image pickup device is increased or the size of a solid-state image pickup device is reduced, a solid-state image pickup device having satisfactory sensitivity can be realized.

Embodiments for carrying out the invention are now described.

This description is made in the following order.

1. First Embodiment (Solid Image Pickup Device)

2. Second Embodiment (Image Pickup Device)

<1. First Embodiment>

A schematic configuration diagram (cross-sectional view) of a solid-state image pickup device according to a first embodiment of the present invention is shown in FIGS. 1A and 1B. 1A shows a cross-sectional view of a face intersecting a transfer gate at a right angle, and FIG. 1B shows a cross-sectional view taken along line AA' of FIG. 1A.

The solid-state image pickup device is configured to form a photodiode (PD) of a sensor unit on the surface of an n ^- semiconductor substrate 1 made of germanium or other semiconductor, and charge transfer in the form of a transfer gate 7. Unit and floating diffusion (FD) 6.

As the semiconductor substrate 1, a semiconductor substrate (a germanium substrate or the like) or a semiconductor substrate and a semiconductor epitaxial layer formed thereon may be used.

A p-type semiconductor well region 2 is formed to be buried in the semiconductor substrate 1.

The semiconductor well region 2 is formed across the entire surface of the pixel region or the entire surface of the wafer of the solid-state image pickup device, and isolates the substrate from the pixel unit. An overflow barrier is formed by means of the semiconductor well region 2.

Individual pixels are isolated by a p ⁺ device isolation region 3 above the semiconductor well region 2. A photodiode (PD) and a charge transfer unit functioning as a sensor unit are formed inside the isolation by the device isolation region 3.

At a portion of the photodiode, an n ⁺ charge storage region 4 is formed, and a p ⁺ positive charge storage region 5 for suppressing a dark current is formed on the surface of the charge storage region 4.

At the charge transfer unit, a transfer gate 7 is formed on the surface of the semiconductor substrate 1 via a thin gate insulating film (not shown) and formed of an insulating layer at the sidewall of the transfer gate 7. Side wall 8.

The transfer gate 7 can be formed, for example, of polysilicon.

In the surface of the device isolation region 3 provided on the left side of the figure, an n ⁺ floating diffusion (FD) 6 is formed.

The floating diffusion 6 and the positive charge storage region 5 of the sensor unit are respectively formed to be set at appropriate positions, wherein the transfer gate 7 is external thereto.

It will be noted that as a variation of the configuration of FIG. 1A, the positive charge storage region 5 can be formed at an appropriate location with the outer edge of the sidewall 8 on the outer side of the transfer gate 7.

A transfer gate 7 is used to transfer charge between the photodiode and the floating diffusion 6. The floating diffusion 6 stores the transferred charge.

The charge storage sub-region is formed under the charge storage region 4 and includes three n-type impurity regions as viewed from below: a first charge storage sub-region 11, a second charge storage sub-region 12, and a third charge storage sub-region 13 .

These charge storage sub-regions 11, 12, 13 are formed above the p-type semiconductor well region 2, that is, at a depth position between the semiconductor well region 2 and the charge storage region 4.

The distance between the p ⁺ device isolation regions 3 becomes narrower at the cross section of Fig. 1B than at the cross section of Fig. 1A, just like the cross section shown in Fig. 5B.

Therefore, with regard to the configuration of the cross section of FIG. 1B, since the effective concentration of the p-type impurity from the device isolation region 3 and the semiconductor well region 2 is increased, the potential is necked at the deep portion of the photodiode.

In order to avoid this, in this embodiment, the first charge storage sub-region 11 (which is the innermost sub-region among the three charge storage sub-regions 11, 12, 13) is formed to extend to the device isolation region 3. That is, the first charge storage sub-region 11 is formed completely across the pixel.

The potential profile at the cross section of Figure 1B is now shown in Figure 2.

Since the first charge storage sub-region 11 is formed to be wide enough to extend to the device isolation region 3, this potential distribution as shown in FIG. 2 can be formed, which extends in the depth direction compared to the potential distribution shown in FIG. .

This is because the effective dose of the n-type impurity in the deep portion of the photodiode can be increased by the wide formation of the first charge storage sub-region 11 so that the surrounding p-type impurity regions 2, 3 can be alleviated. The necking of the potential.

Since the potential distribution can be widened in the depth direction, the depletion layer in the photodiode can be elongated in the depth direction, resulting in improved sensitivity.

More preferably, the first charge storage sub-region 11 formed completely across the pixel is formed at a position not less than 1 μm from the surface of the semiconductor substrate 1.

This enables the depletion layer to extend at a depth of not less than 1 μm, thereby obtaining satisfactory sensitivity to light in the long wavelength region of visible light.

The solid-state image pickup device according to this embodiment can be fabricated in the manner described below.

Initially, as shown in FIG. 3A, a p-type semiconductor well serving as an overflow barrier is formed by ion implantation 21 of a p-type impurity across the entirety of the semiconductor substrate 1 or the entirety of the image pickup region at a specific depth position of the semiconductor substrate 1. 2.

Next, as shown in FIG. 3B, a first charge storage sub-region 11 is formed over the semiconductor well region 2 over the semiconductor well region 2 by ion implantation 22 of n-type impurities.

Next, as shown in FIG. 3C, a resist 23 is used as a mask, and a second charge storage sub-region 12 is successively formed on the first charge storage sub-region 11 by ion implantation 24 of n-type impurities. A third charge storage sub-region 13.

It will be noted that the ion implantation for forming the first charge storage sub-region 11, the ion implantation for forming the second charge storage sub-region 12, and the ion implantation for forming the third charge storage sub-region 13 are performed with different energies. (The order of energy magnitude is first > second > third).

Next, as shown in FIG. 3D, a resist 25 is used as a mask, and a p ⁺ device isolation region 3 is formed by ion implantation 26 of p-type impurities to surround the photodiode of the sensor unit.

At this stage, the implantation amount of the p-type impurity is selected so that the ion-implanted n-type impurity reaches completely across the semiconductor substrate 1. This enables the potential at the boundary region between the device isolation region 3 and the photodiode to be designed to prevent blooming, color mixing, and white point deterioration.

By forming the p ⁺ device isolation region 3 in this manner, the n-type first charge storage sub-region 11 is isolated for each pixel.

Subsequently, as shown in FIG. 3E, a charge storage region 4, a positive charge storage region 5, a floating diffusion (FD) 6, a transfer gate 7, and a sidewall 8 are formed, respectively. These can be formed by techniques known to date.

For example, after the transfer gate 7 is formed, when the transfer gate 7 is used as a mask, the n ⁺ charge storage region 4 is formed by ion implantation of an n-type impurity and ion implantation is performed by p-type impurity. ⁺ positive charge storage area 5. A sidewall 8 made of an insulating layer is formed on the sidewall of the transfer gate 7, and this sidewall 8 is used as a mask, and a floating diffusion (FD) 6 is formed by ion implantation of an n-type impurity.

Thereafter, if necessary, a color filter, an on-wafer lens, and an upper wiring layer may be separately formed.

In this way, the solid-state image pickup device shown in FIGS. 1A and 1B can be fabricated.

According to the solid-state image pickup device of this embodiment, the first charge storage sub-region 11 (which is the lowermost of the three n-type charge storage sub-regions 11, 12, 13) is formed to extend to the device isolation region 3, and thus A charge storage sub-region 11 is formed completely across the pixel. This makes it possible to increase the effective dose of the n-type impurity at the depth of the photodiode, and thus it is possible to reduce the necking of the potential from the surrounding p-type impurity regions 2, 3 to widen the potential distribution in the depth direction.

More specifically, the depletion layer in the photodiode can be elongated in the depth direction and the saturation charge amount can be increased, thereby improving the sensitivity of the photodiode.

Therefore, according to the solid-state image pickup device of this embodiment, if a pixel is miniaturized, satisfactory sensitivity is ensured. Therefore, the number of pixels of the solid-state image pickup device can be increased and the size can be reduced by miniaturization of the pixels.

With the embodiment described above, only the first charge storage region 11 is formed across the pixel, and the second charge storage region 12 and the third charge storage region 13 are formed only at a lower portion of the charge storage region 4.

In the present invention in which a plurality of charge storage subregions are formed under the charge storage region, the number of charge storage subregions formed completely across the pixel is arbitrary.

Thus, in the case where three charge storage sub-regions 11, 12, 13 as shown in FIGS. 1A and 1B are formed, any number of sub-regions can be formed completely across the pixel.

More preferably, the charge storage sub-regions formed entirely across the pixels are configured to be formed over a location that is no less than 1 μm from the surface of the semiconductor substrate 1.

It will be noted that instead of forming a charge storage sub-region completely across the semiconductor substrate or image pickup region as in the manufacturing method described above, ion implantation can be performed while using a mask having an opening for each pixel. A charge storage sub-region formed completely across the pixel is formed.

As in the manufacturing method described above, when the sub-region is formed completely across the semiconductor substrate or the image pickup region and is isolated for each pixel after formation of a device isolation region, formation is easily ensured.

In the above embodiments, although the present invention is applicable to a CMOS type solid-state image pickup device in which floating diffusion (FD) 6 is provided for each pixel, the present invention is also applicable to other types of solid-state image pickup devices.

For example, the present invention is applicable to a CCD solid-state image pickup device as in the aforementioned Japanese Laid-Open Patent Application.

In the above embodiment, the charge storage region 4 is formed as an n-type region in which a p ⁺ positive charge storage region is formed on the surface thereof.

In the present invention, contrary to the above embodiments (with respect to the conductivity type), this configuration including a p-type charge storage region and an n ⁺ negative charge storage region formed thereon is possible. In this case, a plurality of layers of the p-type impurity region are formed under the charge storage region for use as a charge storage sub-region, and at least one or more of the plurality of layers of the p-type impurity region completely span the pixel form.

<2. Second embodiment>

A schematic configuration diagram (block diagram) of an image pickup apparatus according to a second embodiment of the present invention is shown in FIG. This image pickup device includes, for example, a video camera, a digital still camera, or a camera for a mobile phone.

As shown in FIG. 4, an image pickup device 500 has an image pickup unit 501 having a solid-state image pickup device (not shown).

A focusing optical system 502 for incident light focusing and image focusing is provided upstream of the image pickup unit 501. Downstream of the image pickup unit 501, a signal processor 503 is connected, which has a drive circuit for driving the image pickup unit 501 and a signal processing circuit for processing signals photoelectrically converted into images in the solid-state image pickup device. The image signals processed in the signal processor 503 can be memorized in an image memory (not shown).

In this image pickup device 500, the solid-state image pickup device of the present invention, such as the solid-state image pickup device of the embodiment described above, can be used as a solid-state image pickup device.

According to the image pickup apparatus 500 of the embodiment, the solid-state image pickup device of the present invention, that is, a solid-state image pickup device configured to ensure satisfactory sensitivity while advancing pixel miniaturization is used (as described above) ).

This situation is advantageous because if the number of pixels of the solid-state image pickup device is increased or if the size of the solid-state image pickup device is reduced, the image pickup device 500 having satisfactory sensitivity can be configured.

It will be noted that the image pickup apparatus of the present invention is not limited to the configuration shown in FIG. 4, but is applicable to an image pickup apparatus of a type using a solid-state image pickup device.

For example, the solid-state image pickup device may be in the form of being formed into a wafer or may be in the form of a module having an image pickup function, wherein the image pickup unit and the signal processor or the optical system are collectively packaged.

The image pickup device of the present invention can be applied to, for example, a mobile device having a camera or image pickup function and a plurality of image pickup devices. In a broad sense, "image pickup" includes a fingerprint detector and the like.

The present invention should not be construed as being limited to the embodiments described above, and various changes and modifications may be employed without departing from the scope of the invention.

The present invention contains subject matter related to that disclosed in Japanese Priority Patent Application No. 2010-135612, filed on Jun.

It will be understood by those skilled in the art that various modifications, combinations, sub-combinations and changes can be made, depending on the design requirements and other factors, as long as they are within the scope of the appended claims or their equivalents.

1. . . Semiconductor substrate

2. . . P-type semiconductor well region

3. . . Device isolation region

4. . . Charge storage area

5. . . Positive charge storage area

6. . . Floating diffusion (FD)

7. . . Transfer gate

8. . . Side wall

11. . . First charge storage subregion

12. . . Second charge storage subregion

13. . . Third charge storage subregion

twenty one. . . Ion Implantation

twenty two. . . Ion Implantation

twenty three. . . Resist

twenty four. . . Ion Implantation

25. . . Resist

26. . . Ion Implantation

51. . . Semiconductor substrate

52. . . p ^- semiconductor well region

53. . . Device isolation region

54. . . n ⁺ charge storage area

61. . . First charge storage subregion

62. . . Second charge storage subregion

63. . . Third charge storage subregion

500. . . Image pickup device

501. . . Image pickup unit

502. . . Focusing optical system

503. . . Signal processor

1A and 1B are respectively schematic configuration views (cross-sectional views) of a solid-state image pickup device according to a first embodiment of the present invention;

Figure 2 is a potential distribution diagram corresponding to a portion of the cross-sectional view of Figure 1B;

3A to 3E are respectively a program diagram showing a method of manufacturing the solid-state image pickup device of FIGS. 1A and 1B;

4 is a schematic configuration diagram (block diagram) of an image pickup apparatus according to a second embodiment of the present invention;

5A and 5B are respectively schematic configuration diagrams (cross-sectional views) of a solid-state image pickup device having a structure in which a charge storage sub-region is formed under a main charge storage region;

Figure 6 is a potential distribution diagram corresponding to a portion of the cross-sectional view of Figure 5B;

Fig. 7 is a view for explaining a change in potential in the solid-state image pickup device of Figs. 5A and 5B.

1. . . Semiconductor substrate

2. . . P-type semiconductor well region

3. . . Device isolation region

4. . . Charge storage area

5. . . Positive charge storage area

6. . . Floating diffusion (FD)

7. . . Transfer gate

8. . . Side wall

11. . . First charge storage subregion

12. . . Second charge storage subregion

13. . . Third charge storage subregion

Claims (4)

A solid-state image pickup device of a type including a plurality of pixels, each pixel configured to include a sensor unit capable of photoelectric conversion, the image pickup device comprising: a semiconductor substrate; one of a first conductivity type a charge storage region formed in the semiconductor substrate and configured to be the sensor unit and a main charge storage region; a charge storage sub-region made of one impurity region of the first conductivity type, the The charge storage sub-region includes a plurality of layers under the charge storage region in the semiconductor substrate; and a device isolation region in the semiconductor substrate configured to isolate the pixels from each other, the device isolation region is configured by a first An impurity region of one of two conductivity types is formed, wherein at least one charge storage sub-region layer extends across each pixel to the device isolation region. The solid-state image pickup device of claim 1, wherein for each pixel, the charge storage sub-region formed entirely across the pixel is formed at a depth of not less than 1 μm from a surface of the semiconductor substrate. The solid-state image pickup device of claim 1, further comprising a semiconductor well region formed in the semiconductor substrate completely under each pixel under the charge storage sub-region and by one of the second conductivity types Made of impurity areas. An image pickup device comprising: a focusing optical unit that focuses incident light; a solid-state image pickup device comprising a plurality of pixels, each pixel configured to include a sensor unit capable of photoelectric conversion, the solid-state image pickup device further comprising: (a a semiconductor substrate; (b) a charge storage region of a first conductivity type, in the semiconductor substrate and configured to be the sensor unit and a main charge storage region; (c) a charge storage device a region made of one impurity region of the first conductivity type, the charge storage subregion including a plurality of layers under the charge storage region in the semiconductor substrate; and (d) a device isolation region on the semiconductor substrate Configuring the pixels to be isolated from each other, the device isolation region being made of one impurity region of a second conductivity type; wherein at least one charge storage sub-region layer extends across each pixel to the device isolation region, and A signal processor that processes one of the signals obtained by the photoelectric conversion by the solid-state image pickup device.